Recessed burr hole covers and methods for using the same

ABSTRACT

A burr hole cover is configured to be recessed in a burr hole formed in a patient and includes a base and a cap provided with complementary features to allow a portion of a medical device, such as a brain lead, to be situated in the burr hole cover and then secured by rotation of the cap relative to the base. The features include channels on the base and matching cut-outs on the cap, and slots and locking pockets on the base that are configured to be aligned with locking tabs and locking protrusions on the cap. Because the burr hole cover is recessed in the burr hole, the medical device can extend proximally of the burr hole at the level of the cranium. A bottom surface of the cap may be provided with guides for the lead extending distally in towards the brain.

CROSS-REFERENCE TO RELATED APPLICATION(S)

This application is a continuation of U.S. application Ser. No.13/792,165, entitled “Recessed Burr Hole Covers and Methods for Usingthe Same,” filed on Mar. 10, 2013, now U.S. Pat. No. 9,572,973, which isexpressly incorporated by reference herein in its entirety.

BACKGROUND

Field

The present technology relates generally to apparatuses and methods forsecuring a medical instrument, such as a lead, within a burr hole.

Background

Increasingly, leads associated with electrodes or other components thatcan be used for sensing signals from or delivering a form of modulationto a patient's neural tissue are partially implanted in a patient'sbrain through a burr hole that is formed (e.g., using a drill fittedwith a special drill bit) in the patient's cranium (cranial bone orskull). To prepare for forming the burr hole, the scalp over the site isremoved or temporarily retracted. After the burr hole is formed, aportion of a lead is implanted through the burr hole so that electrodesor other components that are associated with the lead are distallylocated at a desired target or targets in the brain. Once a distalportion of a lead is positioned at the target(s), it may be desirable tosecure a proximal portion of the lead in the vicinity of the burr holein the hopes of minimizing the extent to which the distal portion of thelead will shift, for example, away from the target(s), for so long asthe lead is intended to remain implanted in the patient and to functionfor its intended purpose(s).

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A is an exploded perspective view of a burr hole cover and aportion of a medical lead according to an embodiment.

FIG. 1B is a detail of a portion of a base of the burr hole cover shownin FIG. 1A.

FIG. 2A is a schematic view of a patient's skull with a burr hole formedtherein.

FIG. 2B is a schematic view of an electrode-bearing brain leads, atleast one of which has a distal portion thereof implanted in the patientand a proximal portion thereof secured at a burr hole by a burr holecover.

FIG. 3 is a perspective view illustrating a portion of a lead extendingproximally of a burr hole cover, according to an embodiment, after theburr hole cover is installed in a burr hole, in a schematicrepresentation of a portion of a patient's cranium.

FIG. 4 is the perspective view of FIG. 3 showing an additional featureof an insulator covering the installed burr hole cover.

FIG. 5 is a perspective view of a base of a burr hole cover according toan embodiment.

FIG. 6 is a side elevational view of the base of FIG. 5.

FIG. 7 is a top plan view of the base a burr hole cover according to anembodiment.

FIG. 8 is a sectional view taken along the line A-A of FIG. 7.

FIG. 9 is an exploded view of a portion of the sectional view of FIG. 8.

FIG. 10 is a side elevational view of a cap of a burr hole coveraccording to an embodiment.

FIG. 11 is a top plan view of a cap of burr hole cover according to anembodiment.

FIG. 12 is a bottom plan view of a cap of a burr hole cover according toan embodiment.

FIG. 13A and FIG. 13B are top and bottom views, respectively, of a burrhole cover assembly according to embodiments in an unlocked position.

FIGS. 14A and 14B are top and bottom views, respectively, of a burr holecover assembly according to embodiments in a locked position.

FIG. 15 is a schematic view of a user manipulating a cap of a burr holecover according to embodiments relative to a retainer.

The drawings referred to in this description should not be understood asbeing drawn to scale unless specifically noted.

DETAILED DESCRIPTION

Various embodiments are described below, with reference to detailedillustrative embodiments, in the context of burr hole covers. It will beapparent that the apparatuses and methods described herein can beembodied in a wide variety of forms. Consequently, the specificstructural and functional details disclosed herein are representativeand do not limit the scope of embodiments.

Embodiments of a burr hole cover are provided for securing a segment ofa medical device relative to a burr hole formed in the cranium of apatient when a distal portion of the medical device is implanted orotherwise introduced into the burr hole interiorly of the patient. Theembodiments are described primarily with reference to the medical devicebeing an electrode-bearing lead, such as might be used in an applicationfor deep brain stimulation or direct brain stimulation such asresponsive stimulation such as those applications under investigation byNeuroPace, Inc. of Mountain View, Calif. It should be appreciated,however, that the burr hole cover may be used with good results tosecure a segment of a different type of medical device, such as acatheter with an appropriate diameter or other medical instrument,relative to a burr hole prior to and/or during use of the medical devicein its intended application. Similarly, it should be appreciated that,in some circumstances, embodiments of a burr hole cover described hereinmay be used to secure more than one medical device simultaneously (e.g.,two leads) for some applications.

Generally, when a medical device is introduced to a target positioninteriorly of a patient's cranium, it is desirable for the distalportion of the medical device not to move appreciably from that target.More particularly, in the case where the medical device is a deep brainlead with one or more electrodes associated with a distal portionthereof, it is desirable to minimize the degree to which the distalportion moves once it has been positioned at the target. For example, inan application in which one or more of the electrodes are intended to beused in stimulation pathways to deliver a form of electrical stimulationtherapy to the tissue surrounding or adjacent the electrodes, and theelectrodes on the distal portion of the lead are positioned at a desiredtarget area of the patient's brain (for example, the subthalamic nucleus(STN) or a brain location suspected or known to be a focus or related toa focus of an epileptic seizure), it would be desirable to avoid movingthe electrodes from that target area during the time over which it isanticipated the therapy may be delivered. Similarly, in an applicationin which electrodes or other elements associated with the distal portionof a lead are going to be used to sense physiological activity from alocation in the brain, it would be desirable to avoid dislodging thesensors from the desired sensing location once the lead is implanted forso long as sensing potentially may occur.

Applications are known or under investigation in which leads fordelivering stimulation therapy (and/or sensing and/or recording theelectrical activity of nerve cells) are implanted and then left in placefor extended period of time (e.g., on the order of years provided theleads remain intact and uncompromised and otherwise withoutcomplications). Desirably, then, the means and methods by which the leadis discouraged from moving away from the target area will be relativelyrobust and durable and therefore well-suited for chronic or long-lastingapplications involving the lead or other medical device. It may bedesirable to form a burr hole cover from a material or materials thatwill not interfere with any imaging procedure to which the patient mightbe subjected (e.g., materials that will not distort or obstruct animage) and/or from material(s) (e.g., non-magnetic materials) that willnot contraindicate an imaging procedure in the first instance. Inaddition, the material(s) from which the burr hole cover is formeddesirably will not degrade appreciably over time and will bebiocompatible with any body surfaces (e.g., cranial bone) and bodyfluids (e.g., cerebral spinal fluid) with which the burr hole cover maycome in contact throughout the time the burr hole cover is installed inthe patient.

Referring to FIGS. 1-15, embodiments of burr hole covers and embodimentsof methods of using burr hole covers will be described.

FIG. 1A is an exploded view of an embodiment of a two-component burrhole cover 100. The two components are a base 110 and a cap 160. Eachcomponent of the burr hole cover 100 is described in more detail below.

Referring now to FIG. 2A, a burr hole 200 is formed (for example, usinga drill) in a cranial bone or cranium 202 of a patient. The burr hole200 extends from a burr hole top 215 at an outer surface of the craniumto a burr hole bottom 216 at an inner surface of the cranium (towardsthe brain). A burr hole depth 220 can be measured between the burr holetop 215 and bottom 216.

Referring now to FIG. 2B, a burr hole cover 100 is used to secure asegment of a proximal portion 210 of a deep brain lead 203 in a burrhole formed in a cranium 202 of a patient. More particularly, a distalportion 212 of the deep brain lead 203 is shown implanted in the braintissue of the patient, and passing through a burr hole in which a burrhole cover 100 is installed. Exteriorly of the patient's skull, theproximal portion 210 of the deep brain lead 203 is shown arranged on topof the patient's skull.

A hole 230 formed has been formed in the patient's cranium 202 which maybe intended to receive another medical device, such as an implantedneurostimulator (not shown) to which a proximal end (not shown) of thedeep brain lead 203 ultimately may be connected (e.g., for allowingstimulation to be delivered to or physiological activity of the brain tobe sensed and/or recorded).

A second brain lead is also shown in FIG. 2B, namely, a cortical striplead 250. The cortical strip lead 250 has a distal portion that includesa distal strip 256 which contains four disk electrodes 258 that areintended to be implanted so that each rests against a surface oradjacent a surface of the brain. A proximal portion 252 of the corticalstrip lead 250 is shown extending exteriorly of the cranial cavitythrough a stitched-together incision 270 in the patient's scalp ratherthan through a burr hole or via a burr hole cover. It will beappreciated that a cortical strip lead does not have to be routed asshown in FIG. 2B, rather a proximally-extending portion 252 of acortical strip lead may be routed through a burr hole as is the casewith the deep brain lead 203 shown in FIG. 2B.

Referring again to the deep brain lead 203 of FIG. 2, four ringelectrodes 207 are provided at a distal end 214 of the distal portion212 of the deep brain lead 203. In a method according to an embodiment,a surgeon inserts the distal portion 212 of the brain lead 203 in thepatient's brain so that the ring electrodes 207 are in or are adjacent adesired structure or structures or other target in the brain tissue. Thesurgeon may locate the desired implant site for the electrodes using oneor more means such as forms of imaging (e.g., MRI) or microelectroderecordings. The surgeon may manipulate the distal portion 212 of thedeep brain lead 203 to the target location(s) using stereotacticequipment and methods or some other suitable technique or approach.

Once the distal end 214 and its associated electrodes 207 are locatedwhere the surgeon wants them to chronically remain, the surgeon or oneassisting the surgeon grabs (either with fingers or using a surgicalinstrument or tool) the proximal portion 210 of the deep brain lead 203that extends exteriorly of the burr hole 200. Next, the surgeonpositions the base 110 in the burr hole, secures the segment 206 of theproximal lead portion to be secured by the burr hole cover 100 in theburr hole cover, and then inserts the cap 160 into the base 110 andpushes it down in the direction of the brain to affix the lead segment206 relative to the burr hole cover 100.

In embodiments, and referring again to FIG. 1A, the user may orient thelead segment 206 in one of a plurality of possible retaining elements130, such as the four base channels 130 shown in FIGS. 1, 3-5, 7 andFIGS. 13-14. Once the lead segment 206 is oriented in a desiredretaining element 130, the user can line the cap 160 up with the base110 (alignment features may be provided on the base and/or the cap forthis purpose), so that the base channel in which a lead segment 206 hasbeen placed can be matched up with a corresponding cut-out 162 on thecap 160. Desirably, the cap 160 is provided with the same number of capcut-outs 162 as there are retaining channels 132.

After the user has placed the lead segment 206 in a base element 130 andproperly aligned the cap 160 relative to the base, the user may engage alocking mechanism configured using features provided on each of the base110 and the cap 160 to lock the lead segment 206 relative to the burrhole cover 100. The lead segment 206 is thereby restrained, and movementof the distal end 214 of the lead 203 from the location at which it hasbeen implanted in the patient is thereby discouraged.

Optionally, the cap 160 is provided with a plurality of guides 1210 (seebottom view of cap in FIG. 12). A guide 1210 is associated with each capcut-out 162 on a bottom surface 168 of the cap. A guide 1210 associatedwith the cut-out 162 in which the lead segment 206 is secured will tendto discourage the portion of the lead extending distally from the burrhole from being bent at a sharp angle near the bottom of the burr holeand perhaps from pulling away from its intended implant site during theprocess of securing the lead in the burr hole cover 100.

It is contemplated that more than one lead segment 206 or portion ofother medical device may be secured between the cap and base of a burrhole cover according to the embodiments described herein. For example,if a base 110 is provided with four channels 130 and a cap 160 with fourcut-outs 162 corresponding to the four base channels, then the burr holecover may be used to secure two lead segments 206 and possibly as manyas four lead segments 206 (if each channel-and-cut-out combination isoccupied by a lead segment).

Depending on the features with which the base 110 is provided, beforethe distal portion 212 of the lead 203 is implanted in the patient, thebase 110 may need to be threaded over the lead 203 so that the lead ispassing through the cap-receiving aperture 128 (not shown in FIG. 2) ofthe base 110.

After the lead 203 is implanted and the burr hole cover 100 is partiallyor fully installed to secure the lead 203, a proximal end (not shown) ofthe proximal portion 210 of the lead 203 may be routed to and connectedto another implanted device, such as a neurostimulator. Alternatively, aproximal end (not shown) may be connected to a piece of externalequipment that can generate a form of neuromodulation to be communicatedthrough the lead and/or monitor and/or record signals sensed from thepatient's brain via the lead.

Once the components 110 and 160 of the burr hole cover 100 have beeninstalled (which installation is described more fully below), the distalportion 212 of the lead will be discouraged from moving appreciablyrelative to the segment 206 of the proximal lead portion 210 that issituated in the burr hole cover 100, even when the proximal portion 210that extends proximally away from the point of affixation at the burrhole cover 100 is manipulated (for example, when the surgeon attaches aproximal end to another device internally or externally of the patientor when the patient fiddles or fusses with the proximal portion 210during the time when the lead remains chronically implanted in thepatient.)

Optionally, after the burr hole cover 100 has been installed and beforeor after the proximal end of the proximal portion 210 of the lead 203has been routed to wherever it is to be connected, and referring now toFIG. 4, an insulator 410 may be disposed over the installed burr holecover 100 to protect some part of the proximally-extending portion 210of the lead 203 as it exits the burr hole cover 100. The insulator 410may be formed from a relatively pliant material, such as silicone, andattached to the cranium using screws and/or adhesive or some other meansof attachment.

When the lead 203 is intended to remain in place chronically, after theprocedure to implant the lead is completed and the burr hole cover 100is installed, the burr hole cover 100 (or the burr hole cover 100 andinsulator 410, if an insulator is used) may be re-covered with theretracted or removed section of scalp or with a prosthetic or syntheticscalp substitute.

When the medical device being secured is an electrode-bearing brain leadsuch as the lead 203, one or more conductors may be provided in the leadto permit electrical connectivity between the electrodes on the distalend 214 and a lead proximal end (not shown) that ultimately is connectedeither to another implanted device, such as a neurostimulator, or to anexternal component not implanted in the patient. If there are multipleconductors in a lead 203, the conductors may be insulated from eachother within the body of the lead 203. If the lead 203 (or other medicaldevice) is to be introduced into brain tissue, the lead 203 may beformed from materials that render it more malleable or floppy thanstiff, for example, to minimize the likelihood that the lead willinterfere with the tissue in which (or against which) it is implanted orotherwise cause trauma at and around the implant site. In a case where alead 203 is not inherently stiff, the lead 203 may be provided with alumen or cavity that extends almost all of the way through or justpartially through the body of the lead to accommodate a stiffener, suchas a stylet, which can remain in place during the procedure to implantthe lead and thereafter can be removed.

If the medical device to be secured with a burr hole cover includesconductors, then the risk of compromising the conductors (e.g., breakingor overstressing the conductors) either during or subsequent toinstallation of the burr hole cover desirably should be minimized.Similarly, if the medical device is a lead that is not inherently stiffbut has its stiffness supplemented with a stiffener such as a styletthat is ultimately intended to be withdrawn and removed from the lead,then the burr hole cover will need to be adequate to affix the lead inthe vicinity of the burr hole with the stylet absent from the lead body.In some cases, it may be desirably to affix the lead with the burr holecover before withdrawing the stylet (for example, to minimize thelikelihood that the distal portion of the lead will be dislodged fromthe intended target area during the affixation process). In other cases,it may be desirable to affix the lead with the burr hole cover after thestylet has been removed from the lead body (for example, to avoid thepossibility that an installed or partially installed burr hole coverwill interfere with withdrawing the stylet from the lead body or willresult in unintended movement of the distal portion of the lead).Depending on the features with which the burr hole cover 100 isprovided, any stylet may need to be withdrawn proximally from the leadpast the segment 206 that is to be secured in the burr hole cover 100before the segment can be secured.

In addition to the nature of the medical device (e.g., lead withconductors extending therethrough or some other type of medicalinstrument such as a catheter) and the relative stiffness of the medicaldevice (e.g., whether it is stiff or has a removable stiffener), anothercriterion for selecting a burr hole cover is the degree of securitydesired at the segment 206 of the proximal lead portion 210 to besituated in the burr hole cover 100. For example, in some applications,it may be undesirable for the distal portion 212 of a lead 203 to movemore than a fraction of an inch once the distal end 214 has beenpositioned at a target area. This might be the case where one or moreelectrodes (such as one or more of the electrodes 207) are intended toremain at or near a relatively small physical target in the brain (e.g.,the STN). In other applications, it may be acceptable for the distal end214 of the lead 203 to shift or migrate more over the period of time inwhich the lead remains implanted in the patient (e.g., when electrodesare being used to stimulate or sense from a broader physical target areaor to stimulate or sense at some point in a functional pathway (such asa known or suspected brain circuit), as contrasted to a physicalstructure). In some applications under investigation that use animplanted neurostimulator together with one or more implantedelectrode-bearing leads to treat epilepsy, more potential movement ofthe distal end 214 of the lead 203 may be tolerable than in otherapplications, such as an application using deep brain stimulation totreat the symptoms of a movement disorder.

In still other circumstances, one factor in selecting a burr hole coverto use for a particular patient may be the profile of the burr holecover 100, that is, the extent to which the burr hole cover willprotrude from the patient's cranium 202 once it has been installed. Theprofile consideration may be directly or indirectly related to thenature of the medical device the burr hole cover 100 is being used tosecure. For example, a user may want to avoid causing sharp bends orangles in a lead with conductors running through it to minimize the riskof compromising the function of the lead or any electrodes with whichthe lead is associated. The profile of a burr hole cover may help theuser to minimize such sharp bends. The profile of a burr hole cover mayalso be relevant for aesthetic reasons, for example, so that the burrhole cover cannot readily be perceived by others (for example, ascontrasted to a burr hole cover that produces a noticeable bump underthe scalp in a bald patient). Finally, there may be practical reasonsthat drive selection of a burr hole cover with a particular profile: forexample, patients may be more likely to “fiddle” with a higher profileburr hole cover and any associated lead(s) or other medical devices thatare secured by it simply because the patient is likely to notice theburr hole cover more.

Referring now to FIGS. 1-15, embodiments of a burr hole cover 100 arecharacterized by a base 110. The base 110 is provided to be generallycircular in shape with a circumference that is slightly less than thecircumference of the burr hole 200 with which the burr hole cover 100 isto be used. More particularly, since in use the base 110 of the burrhole cover 100 will be inserted well into the burr hole 200, thecircumference of the base 110 should not exceed the likely circumferenceof the burr hole with which it is to be used. Burr holes 200 are oftendrilled with special drill bits which are configured to form afenestration in the cranial bone with predetermined approximatedimensions (e.g., a 14 mm diameter circular hole). Thus, in embodimentsof the burr hole cover 100 described here, the dimensions of the base110 and cap 160 components for a given burr hole cover 100 may beselected to be slightly smaller than the dimensions of standard-sizedburr holes, so that a variety of commonly-sized burr holes may beaccommodated.

The base 110 is provided with a pair of pads 112 extending out from thecircumference of the base. Each pad 112 may be provided with an aperture114 configured to receive a bone-attaching element (such as the bonescrews 1310 shown in FIGS. 13A and 14A) with which to attach the base110 to the patient's cranium 202. As best shown in FIG. 6, each pad 112may be slightly offset by a height or distance 610 measured from a topsurface 600 of the base 110 (i.e. the surface of the base that will faceaway from the brain when the base is installed in the burr hole 200).The offset distance 610 is provided so that the entirety of the base 110except for the pads 112 for attaching the base to the cranium 202 can besituated in a plane that is at or below the top surface of the burr hole200. With the base 110 recessed in the burr hole 200 in this manner, theburr hole cover 100 essentially has no profile above the burr hole savefor pads 112.

In other embodiments, the burr hole cover 100 may be provided withfeatures other than the pads 112 for securing the base 110 and/or thecap 160 to the cranium 202. Such features may include elementsconfigured to allow the base to be anchored to the interior of the burrhole 200, such that no part of the base 110 is configured to extendabove the exterior-facing surface of the burr hole 200.

Referring especially to FIGS. 2A and 6, the base 110 is characterized bya depth or thickness 612 that is selected to be equal to or less thanthe burr hole depth 220. The base thickness 612 corresponds to thedistance traversed between the top surface 600 of the base 110 and abottom surface 614 (i.e., the surface intended to face interiorly of theburr hole when the burr hole cover is installed). As the base 110 isconfigured to seat interiorly of the burr hole 200 formed in the patient(except for the pads 112, if pads 112 are provided), when the base 110is installed, the thickness 612 will traverse some or all of thedistance between the outermost surface of the cranium and the innermostsurface of the cranium (i.e., the surface of the cranial bone closest tothe brain). Thus, the base thickness 612 may be provided with adimension that generally corresponds to the thickness of the averageperson's cranial bone in a given area of the skull (or, put another way,to the average burr hole cover depth 220). Preferably, the thickness 612will be selected so that when the burr hole cover 100 is completelyinstalled, no component of the burr hole cover 100, including the base110 or the cap 160, will extend further in towards the brain by adistance greater than the thickness of the cranial bone where the burrhole 200 has been formed. Since every patient's skull thickness may bedifferent, and burr holes may be drilled in different parts of apatient's skull, the thickness 612 should be selected to suit multiplepossible cranial bone thicknesses. Alternatively, bases with a varietyof thicknesses may be provided in order to accommodate differentpatient's skull thicknesses.

The base 110 is characterized by an outer perimeter 108 along thecircumference thereof and is provided with a cap-receiving aperture 128circumscribed by an inner perimeter 109. The base 110 is characterizedby a width 129 corresponding to the distance the base traverses betweenthe outer perimeter 108 and the inner perimeter 109. The base 110 may beselected to be wide enough to provide stability to the burr hole cover100, but not so wide as to encroach too significantly upon the amount ofworking space. That is, the space defined by the cap-receiving aperture128 is the space in which a user is able to manipulate the lead or othermedical device to be secured by the burr hole cover to, for example,orient a lead segment 206 in one of the retaining elements 130. The baseshould be just wide enough to stably anchor the burr hole cover assemblyin the burr hole so that the user has the maximum possible room tomaneuver the lead during the installation process.

In some embodiments, the base 110 may be provided with ridges or threads(not shown) on an outer surface thereof to encourage the base 110 toengage with a surface of the cranial bone exposed by the drilling of theburr hole and therefore further stabilize the base 110 relative to theburr hole 200.

The base 110 is provided with a plurality of retaining elements 130 andat least two alignment features 134. In some embodiments, the shape andcontour of each retaining element 130 is configured to cooperate with acorresponding cut-out 162 provided on the cap 160, so that when aretaining element 130 such as a base channel of the base 110 is alignedwith a cap cut-out 162 of the cap 160, the mating of the base channel130 and the cut-out 162 forms an approximately cylindrical or ellipticalaperture 310 through the base 110 (see, e.g., FIG. 3 and FIGS. 13A-13B).Desirably, the diameter of the mated aperture 310 is large enough toallow the medical device the burr hole cover is designed to secure(e.g., a cylindrical brain lead) to move freely within the matedaperture 310.

The alignment features 134 of the base 110 are provided to assist a userin placing the cap 160 in an initial position (as shown in FIGS.13A-13B) relative to a base 110 that has been previously situated in aburr hole 200 (as for, by example, using bone screws in the padapertures 114). The alignment features 134 may comprise a pair of slotsthat are disposed opposite each other on an inner surface of the base110. Referring now to FIG. 1B, each slot 134 may be defined by a leftedge 176 and a right edge 178 and extends from the top surface 600 tothe bottom surface 614 of the base 110. Near the bottom surface 614,each slot 134 widens into a square or rectangularly-shaped lockingpocket 180 of the base 110. In the embodiments shown, each slot 134widens into a locking pocket 180 that extends from the left edge 176 ofthe slot, owing to the manner in which the locking mechanism for theseembodiments is configured, as is further described below. Each lockingpocket 180 may be characterized by a near edge 182 which is common witha portion of the left edge 176 the relevant slot 134 and a far edge 183.

The base 110 may be formed from a material that is relatively rigid suchas a plastic or polymer (e.g., poly-ether-ether-ketone or PEEK). Thematerial should be non-toxic in the event in comes into contact withbodily fluids or tissue and should be long lasting when implanted in acranial burr hole. The material may be clear or opaque so that thecontours of the burr hole 200 may be perceived while the base 110 isbeing situated. Alternatively, the base 110 may be formed from a moreresilient or pliable material, such as silicone rubber. Such a moreresilient material may assist in managing the stresses and strainsplaced on the medical device both during and after the burr hole coveris installed to fix a segment of the device relative to the burr hole.

Referring now especially to FIG. 1A and FIGS. 10-11, a cap 160 accordingto embodiments is further described. The cap 160 is characterized by atop surface 164 and a bottom surface 168, a plurality of cut-outs 162extending through the cap top surface 164 to the cap bottom surface 168and each configured to mate with a retaining element 130 of the base110, a pair of alignment features 184 configured to align with acorresponding pair of alignment features 134 in the base, a pair oflocking features 186, and a plurality of guides 1210, such as leadguides, provided in the cap bottom surface 168.

The cap 160 is designed to fit entirely within the circumference of thebase 110, such that all parts of the cap rest within the bounds of thebase outer perimeter 108 when the cap is fitted into the base. Similarto the base thickness or depth 612, and as illustrated in FIG. 10, thecap 160 is characterized by a thickness 1010 measured as a distancebetween the cap top surface 164 and the cap bottom surface 168. The capthickness 1010 is desirably designed so that, when the cap 160 is fittedinto the base 110, the top surface 164 of the cap will be approximatelyin the same plane of the top surface of the base 600. Put another way,the burr hole cover 100 when fully assembled with the segment of themedical device it is meant to secure will be entirely recessed withinthe burr hole 200 save for any bone-attaching pads 112 offset above andextending away from the base top surface 600. Alternatively, the capthickness 1010 is specified so that when the cap 160 is fitted into thebase 110, the cap top surface 164 will not sit appreciably higher thanthe top 215 of the burr hole 200 itself.

Each cap cut-out 162 is provided with a semi-circular indentation 192and a radius 194. Each cut-out 162 is configured to match up with acorresponding retaining element 130 in the base 110 (such as a basechannel) to form a mated aperture 310. As alluded to above, the diameterof the mated aperture 310 desirably is slightly greater than thediameter of the medical device (e.g., a lead) the burr hole cover 100 isused to secure. (It will be appreciated that in alternative embodiments,the shape of an aperture 310 formed by the mating of a retaining element130 in the base and a cut-out 162 in the cap may be different, such asif the medical device to be secured with the burr hole cover is notcylindrical as typically is a brain lead.)

Each alignment feature 184 of the cap 160 is provided in the samevertical plane as a corresponding cap locking feature 186. As can bebest seen in FIGS. 1A, 10, and 11, the alignment features 184 areprovided as tabs that extend outwardly and upwardly from a circumferenceof the cap 160 near the top surface 164 of the cap. The locking features186 are provided as locking protrusions that extend outwardly from thecircumference of the cap 160 near the bottom surface 168 of the cap.Each alignment tab 184 and its vertically aligned locking protrusion 186are configured to slide within a corresponding slot 134 of the base 110.Therefore, neither the cap alignment feature 184 nor the cap lockingfeature 186 is provided with a dimension that would preclude it fromfitting in the corresponding alignment feature 134 in the base 110. Forexample, neither the cap alignment tabs 184 nor the cap lockingprotrusions 186 are provided to be wider than the narrowest dimension ofthe corresponding alignment slot 134 in the base 110.

When the cap 160 is positioned relative to the base 110 so that both ofthe alignment tabs 184 are lined up with the corresponding slots 134 inthe base 110, then the cut-outs 162 in the cap 160 will be mated withthe corresponding channels 130 in the base, including the base channel130 in which the user has situated the lead segment 206.

To lock the cap 160 relative to the base 110 and to thereby secure thelead segment 206, the user rotates the cap 162 in the direction of theradius 194 of the cut-out 162. In the embodiments shown in the figures,this direction is clockwise or to the right. When the cap 160 is rotatedrelative to the base 110, the cut-out radii 194 will slide to the right,and the cut-out radius 194 in the mated aperture 310 in which the leadsegment 206 has been situated will be pressed into contact with thebase. Also when the cap 160 is rotated, each locking protrusion 186 willslide into its corresponding locking pocket 180 in the base. When thecap 160 is rotated so far that the locking protrusions 186 abut the faredges 183 of the locking pockets 180, the far edges 183 of the lockingpockets will act to resist any further rotation. Thus, when the lockingprotrusions have been stopped by the far edges 183 of the lockingpockets, the cap 160 will be at its final position within the base 110and the lead segment 206 will be locked into place in the burr holecover 100.

It will be appreciated that a cap and base according to embodiments maybe provided with elements and features, including base retainingelements and cap cut-outs, base alignment slots and cap alignment tabs,and base locking pockets and cap locking protrusions, that allowrelative movement of the cap and base in other directions to secure aportion of a medical device in the burr hole cover.

The cap top surface 164 preferably is provided with one or morerecessions 163 for receiving a surgical tool (preferably a commonsurgical tool such as forceps or tweezers) which a user can rely upon tohold and manipulate the cap 160 during a process of installing oruninstalling the cap in the burr hole cover 100 (see also FIG. 15).Alternatively, the cap 160 may be designed for use with a custominstallation tool, in which case the features provided in the cap 160for facilitating installation will be suitable for use with, and perhapsunique to, the custom installation tool. (It will be appreciated thatfeatures to improve the ease with which the surgeon can manipulate thecap relative to the other components of the burr hole cover may also berelied upon to remove the cap, for example, in the process of removingor replacing a previously implanted lead that has been secured with theburr hole cover.)

As with the base 110, the cap 160 may be formed from a material that isrelatively rigid such as a plastic or polymer (e.g.,poly-ether-ether-ketone or PEEK). The material should be non-toxic inthe event it comes into contact with bodily fluids or tissue and shouldbe long lasting when implanted in a cranial burr hole. The material maybe clear or opaque so that, for example, the lead segment 206 and theportion of the lead extending distally of the lead segment 206 may beperceived by the user while the cap 160 is aligned and locked intoposition in the base 110 and thereafter. Alternatively, the cap 160 maybe formed from a more resilient or pliable material, such as siliconerubber. Such a more resilient material may assist in managing thestresses and strains placed on the medical device both during and afterthe burr hole cover is installed to fix a segment of the device relativeto the burr hole. For example, silicone rubber may be less likely topinch a portion of a lead against the burr hole cover in a manner thatcomprises the lead's functionality.

It is noted that the surfaces that characterize the various elements andfeatures of the base 110 and cap 160 that are designed to contact aportion of the lead or other medical device with which the burr holecover 100 is to be used collectively are configured to minimize thestresses placed on any lead segment 206 (or segment of another medicaldevice) that may be secured by the burr hole cover 100 after it isinstalled, and, for that matter, the stresses placed on other parts ofthe lead 203 (such as the proximal portion where the lead exits the burrhole cover at the skull). For example, the portion of the lead that iscaptured in the burr hole cover 100 is relatively small compared to theoverall length of the lead, so a relatively small portion of the lead issubjected to stress within the burr hole cover.

Referring now primarily to FIGS. 13-15, a method of using a burr holecover according to some embodiments will be described. A lead 203 (orother medical instrument such as a catheter) may be partially implantedin the patient so that a distal portion of the lead 212 (or othermedical instrument) extends distally from the burr hole 200 towardsand/or into the patient's brain (see, e.g., the direction represented bythe arrow E in FIG. 3) and a proximal portion 210 of the lead (or othermedical instrument) extends proximally from the burr hole away from thepatient's brain (see, e.g., the direction represented by the arrow F inFIG. 3).

By the time the lead is implanted, the base 110 may previously have beensituated at the location of the burr hole 204 so that the lead 203 ispassing through the cap-receiving aperture 128. If the base 110 isprovided with pads 112 for attaching the base 110 to the cranial bone,then the base 110 can be secured to the patient's cranium 202 using bonescrews or other appropriate bone-attaching elements. Depending on theconfiguration of the base 110, it may be secured to the cranium 202 byother or additional means, such as an adhesive. Alternatively, if thebase 110 is provided with a feature for slipping the base 110 around alead 203 (e.g., a slit provided in the base (not shown in the figures)),then the base 110 can be situated at the location of the burr hole evenafter the lead has been implanted and a portion of the implanted lead isextending proximally out of the burr hole.

When the user is placing the base 110 in the burr hole 200, the user cansituate the base 110 so that any retaining elements 130 are oriented ina particular direction relative to the patient's cranium and any otherimplanted or external device to which the implanted lead 203 is to beconnected.

The base 110 is designed to be recessed in the burr hole 200. The usermay situate the base 110 inside the burr hole using his or her fingersor an appropriate surgical tool. If the base 110 is provided with pads112 that are vertical offset from and extend away from the top surface600 of the base 110, then the pads 112 may assist in preventing the basefrom inadvertently passing all the way through the burr hole and intothe cranial cavity.

Depending on where the user wants the proximal portion 210 of the lead203 to ultimately be located, e.g., dressed out of the burr hole in ananterior direction (such as towards the patient's nose) or dressed outof the burr hole in a posterior direction (such as towards the patient'sback), the user can selected one of the base channels 130 in which tosituate the lead segment 206.

When the surgeon is ready to position the lead segment 206 in the base110, if the lead 203 has been provided with a stiffener such as a styletwhich has not yet been removed, then the stiffener desirably is removedat this point. Then, once the user has selected a base channel 130 touse, the surgeon may move the lead 203 around in the working spacedefined by the cap-receiving aperture 128 until the surgeon has decidedupon a base channel 130 in which to situate a proximal portion 210 ofthe lead at the burr hole, i.e., lead segment 206. Once the lead segment206 is situated in a desired channel 130, the surgeon can then hold (orhave one assisting hold) the proximally-extending portion 210 of thelead 203 out of the way while the surgeon positions the cap 160 relativeto the base 110. In embodiments in which the channel is notcharacterized by a diameter that is smaller than the diameter of thelead 203, the lead segment 206 will be simply resting in the selectedchannel 130 at this stage, and not be secured there by reason of apress- or friction-fit.

After the base 110 is installed in the burr hole 200 and the leadsegment 206 situated in a base channel 130, the user positions the cap160 over the cap-receiving aperture 128 and aligns the alignment tabs184 of the cap 160 with the alignment slots 134 of the base 110. FIGS.13A and 13B are top and bottom views, respectively, of the cap 160 andbase 110 in this initial, unlocked position with the cap alignment tabs184 lined up with the base slots 134. The surgeon may accomplish placingthe cap 160 in this initial position relative to the base 110 by usingforceps placed in the cap recessions 163 to grab and hold the cap 160while the cap is being manipulated relative to the base 110 (see FIG.15).

Because the cap locking protrusions 186 are in the same vertical planeas the cap alignment tabs 184, when the cap alignment tabs 184 arealigned with the base slots 134 and the cap 160 is pressed into the base110, the cap locking protrusions 186 near the bottom surface 168 of thecap 160 will slide into the slots 134 toward the bottom surface 614 ofthe base. Each cap cut-out 162 will match up with its correspondingchannel 130 in the base 110 to form a mated aperture 310, and one of themated apertures so formed will contain the lead segment 206.

The guides 1210 provided in the cap bottom surface 168 encourage theportion of the lead extending distally of the lead segment 206 tomaintain a gentle curve or bend throughout the time the cap is beingmanipulated relative to the base 110. More particularly, the guide 169associated with the base channel 130 and cap cut-out 162 that will berelied upon to secure the lead in the burr hole cover 100 may tend todiscourage sharp angles in the lead and/or tugging or pulling on thelead that might move the distal end of the lead from its intendedimplant location.

To move the cap 160 into its final position relative to the base 110,the user rotates the cap 160 (still using the forceps in the caprecessions 163 if provided) in a clockwise direction. When the cap 160rotates to the right, the radii 194 of the cap cut-outs 162 will moveinto the space defined by each base channel 130. FIGS. 14A and 14B aretop and bottom views, respectively, of the burr hole cover with the capin its final, locked position relative to the base, i.e., with the caprotated to the right. This rotational movement of the cap 160 afteraligning it with the base 110 will cause the lead segment 206 in thebase channel that contains it to be pressed between surfaces of the cap160 and the base 110. The same rotational movement will cause thelocking protrusions 186 near the bottom surface 168 of the cap 160 tomove into their corresponding locking pockets 180 near the bottomsurface 614 of the base 110. When each locking protrusion 186 reachesthe far edge 183 of the locking pocket 180 of the base 110, then anyfurther rotation of the cap 160 relative to the base 110 will beresisted in either direction. That is, further rotation in the clockwisedirection will be resisted because the stops represented by the caplocking protrusions 186 reaching the far edges 183 of their respectivebase locking pockets 180 will have been encountered. Rotation back inthe counterclockwise direction will be resisted because the cap lockingprotrusions 186 are now situated in their respective base lockingpockets 180. Accordingly, the lead segment 206 at this point will besecured in the burr hole cover 100.

The surgeon may now dress the portion of the lead extending proximallyof the burr hole cover 100 in any desired manner. Because the topsurface 164 of the cap and the top surface 600 of the base 110 bothshould be recessed within the burr hole so that the top surfaces 164,600 are at approximately the same level as the top 215 of the burr hole200, the proximally-extending portion 210 of the lead 203 should not beforced to bend in any sharp angles from the point at which the leadsegment 206 is secured in the burr hole cover 100.

The surgeon may connect a proximal end (not shown) of the lead 203 toanother implanted or external device or otherwise arrange the lead sothat it might be proximally connected in a subsequent procedure.Optionally, the user can further dress a portion of the lead extendingproximally of the burr hole cover 100 on the patient's skull by, forexample, tacking the lead down to the cranial bone with a staple orsuture or the like. This may be accomplished before or after the burrhole cover 100 is completely installed (i.e., before or after the cap160 has been fitted into the base 110 or locked into the base 110.).More often than not, however, this further lead dressing will occurafter the surgeon has finished installing the burr hole cover. Thesurgeon may coil up the remaining proximal portion of the lead andreplace the patient's scalp over the surgical field, with the intentionof connecting a proximal end of the lead (not shown) to externalmonitoring equipment or a test stimulator or to another implantedmedical device, such as an implanted neurostimulator.

In the event it becomes necessary or desirable to remove a burr holecover 100 or a lead segment 206 from a burr hole cover, the lead segment206 can be released by rotating the cap 160 counterclockwise (or to theleft) relative to the base 110, for example, by placing forceps in thecap recessions 163.

Thus, embodiments provide for securing a lead to a burr hole with atwo-component burr hole cover have been described which avoid sharptransitions and edges on either side of the burr hole and which providevirtually no profile extending above the top of the burr hole exceptperhaps for bone-attaching pads that are vertically offset from a topsurface of the base of the burr hole cover. A relatively small portionof the lead or other medical device is fixated in the burr hole cover ascompared to the overall length of the lead or other medical device.Thus, the stresses on the lead or medical device are controlled at thepoint of fixation.

Various example embodiments are thus described. All statements hereinreciting principles, aspects, and embodiments as well as specificexamples thereof, are intended to encompass both structural andfunctional equivalents thereof. Additionally, it is intended that suchequivalents include both currently known equivalents and equivalentsdeveloped in the future, i.e., any elements developed that perform thesame function, regardless of structure. The scope, therefore, is notintended to be limited to the embodiments shown and described herein butrather is defined by the appended claims.

What is claimed is:
 1. A burr hole cover for securing a portion of amedical device within a burr hole formed in a patient's cranium, theburr hole cover comprising: a base provided with a cap-receivingaperture, a plurality of base channels, and at least one slot having alocking pocket provided in the at least one slot of the base; and a capprovided with a corresponding cut-out for each channel of the pluralityof base channels provided in the base, and a locking protrusiondimensioned to fit within the at least one slot of the base, wherein thecap is configured to be placed in the cap-receiving aperture and totransition, through rotational movement of the cap relative to the base,between 1) an unlocked position during which the locking protrusion isvertically aligned with an axis of the at least one slot and the lockingprotrusion is disengaged from the locking pocket of the at least oneslot of the base, and 2) a locked position during which the lockingprotrusion is offset from the axis of the at least one slot and thelocking protrusion is engaged with the locking pocket of the at leastone slot of the base.
 2. The burr hole cover of claim 1 wherein the capfurther comprises at least one recession configured to receive asurgical tool to assist in manipulating the cap relative to the base. 3.The burr hole cover of claim 1 wherein the base is characterized by abase circumference and further comprises at least one pad verticallyoffset from and extending away from the base circumference.
 4. The burrhole cover of claim 3 wherein the at least one pad has a bottom surfacealigned with a top surface of the base such that when the base ispositioned in the burr hole, the top surface of the base is situated ina plane that is at or below a surface of the cranium at the burr hole.5. The burr hole cover of claim 1 wherein the cap is provided with aplurality of guides in a bottom surface of the cap, each guidecorresponding to one of the channels in the plurality of base channels.6. The burr hole cover of claim 5 wherein each of the plurality ofguides is further configured to contact a length of the medical deviceduring or after the burr hole cover is installed in the patient.
 7. Theburr hole cover of claim 1, wherein each channel and the correspondingcut-out are horizontally aligned with each other when the cap is in theunlocked position.
 8. The burr hole cover of claim 7, wherein eachchannel and the corresponding cut-out form an aperture when the channeland the corresponding cut-out are horizontally aligned, the apertureconfigured to receive the medical device.
 9. The burr hole cover ofclaim 1, wherein each channel and the corresponding cut-out arehorizontally offset from each other when the cap is in the lockedposition.
 10. The burr hole cover of claim 9, wherein a radius of thecorresponding cut-out is configured to engage the medical device whenthe channel and the corresponding cut-out are horizontally offset.